There are many electronic devices to enhance our working efficiencies every day such as cellular phones, notebook computers, personal digital assistants (PDA), etc. Since the competitions among the same businesses are getting intense, trade secrets have drawn many attentions these days. Therefore, there are more and more electronic devices have included security screening devices such as fingerprint sensors to ensure the trade secrets will not be leaked out to the opponents, and only the owners of the electronic devices can initiate the electronic devices and access to the information inside the electronic devices through the scanning of their fingerprints. Moreover, with the fingerprint sensors added to these electronic devices, the market values of these electronic devices will be higher.
So far fingerprint sensors are fabricated by semiconductor processes and then assembled. The packages for fingerprint sensors are different from the conventional packages where the fingerprint sensor packages have exposed sensing areas for fingerprint recognition.
As shown in FIG. 1 and FIG. 2, a conventional fingerprint sensor package 100 is a BGA (Ball Grid Array) configuration and includes a substrate 110, a fingerprint sensor chip 120, a plurality of bonding wires 130 and an encapsulant 140. A sensing area 123 is formed on the active surface 121 of the fingerprint sensor chip 120. The back surface 122 of the fingerprint sensor chip 120 is attached to the top surface 111 of the substrate 110. The fingerprint sensor chip 120 is electrically connected to the substrate 110 by the plurality of bonding wires 130. The encapsulant 140 is formed on the top surface 111 of the substrate 110 by molding to encapsulate the bonding wires 130 and some portions of the fingerprint sensor chip 120 with the sensing area 123 exposed from the encapsulant 140. A plurality of external terminals 150 such as solder balls are disposed on the bottom surface 112 of the substrate 110 so that the fingerprint sensor package 100 can mechanically and electrically connect to an external printed circuit board by SMT, not shown in the figures, where all the mechanical and electrical connections are established at the bottom surface 112 of the substrate 110. Therefore, the overall thickness of the fingerprint sensor package 100 can not be reduced due to the heights of the external terminals 150 after SMT and the molding encapsulant 140. Moreover, during fingerprint recognition, the fingers will exert extra stresses on the fingerprint sensor chip 120 where the extra stresses will transmit to the bottom of the substrate 110 to break the external terminals 150 leading to electrically open.
In Taiwan R.O.C. Patent No. I243437, entitled “Sliding type thin fingerprint sensor package”, a fingerprint sensor package is revealed. The back surface and sides of the fingerprint sensor chip is pre-molded by a molding protection layer, then a flexible printed circuit board is attached to the bonding pads disposed on one side of the fingerprint sensor chip, i.e., the encapsulation of the fingerprint sensor chip is done first then the attachment of the flexible printed circuit board is followed. However, there is a risk of contamination of the sensing area during encapsulation, moreover, the existing packaging processes and equipment can not be implemented.